A traditional solution in the purpose described above and particularly in square shaped basins is of the kind that a fluid processing apparatus, such as a clarification basin or like, comprises usually a special kind of a scraper bar arrangement, which has several scraper bars, existing one after the other in a longitudinal direction of a basin, and movement means for moving the same, such as two chains, being placed parallelly and being driven by means of a drive wheel and idle wheel assembly, in connection with which the scraper bars are fastened removably particularly in order to make easier the service and maintenance of the scraper bar arrangement. The type of scraper bar arrangements mentioned above are nowadays being used e.g. in connection with clarification basins in a way that the scraper bar/bars is/are transferred by chains, moving at opposite side or intermediate walls of the basin, alternatively on the surface and at the bottom of the basin, scraping sludge existing at the bottom to a sludge pocket while passing along the bottom, and, respectively guiding material existing on the surface to a collecting chute, which goes crosswise over the basin, while passing on the surface. There are also scraper bar arrangements, in which the bars are being moved e.g. by means of a carriage, moving above the basin, or e.g. by hydraulic arrangements. Also the shape of the basin may be in practice almost of whatever form. For example in circular basins a so called bridge scraper arrangement is a very usual solution for moving of surface scum.
In this connection, the surface scum is traditionally exhausted in a so to speak indirect manner, whereby the scrapers while passing on the surface, guide the material on the surface towards the collecting chute in a so called free-drifting manner. The collecting chutes, being used in this connection, are usually mechanically operated “suction chutes”, which are being rotated from time to time around a longitudinal axis to a position, in which the surface scum is being “gulped” inside the same in order to lead it subsequently away from the liquid basin. On the other hand, in this connection a suction chute is used also, which has a moveable front wall, the operating principle of which is, however, in practice the same as described above.
A problem related to this kind of suction chutes is that they take along too much surface water, which can thus drift along with the surface scum furthermore to the exhaust channel of the surface scum. Also the bearing of such rotating suction structures to the walls of the basin is very difficult to carry out structurally, which is why among other things leakages are caused. In addition to the above, the suction chutes easily tend to get jammed among other things due to temperature differences. The type of mechanically operated chute arrangements described above require naturally also operating devices and automation in order to move the chutes, which is why this kind of implementations require a very dense service and maintenance in order to keep them operable. Furthermore, a problem in practice related to this kind of solutions is due to excessive surface scum getting collected on the surface of the liquid basin, together with which also other impurities may get collected. It is thus very usual that also organic processes may take place in the surface scum among other things in the form of algal growth.
For example in publication JP 102 773 11 there has been presented a solution applicable for the type of purpose described above, for being used for example in a so called clarification basin, which is based on an overflow of the surface scum taking place in successive phases. On the other hand a solution of a corresponding type in this respect may also be found from international publication WO 94/04464, which solution is meant for separating of oil or oil-containing substance from water by successive overflow discharges.
In this context also utilization of downwards sloping guiding surfaces has been suggested in the overflow discharge of the surface scum from one process space to another. In practice such a problem is involved with both of the above solutions that by principles represented therewith it is not possible to control the amount of water getting drifted along with the surface scum to be exhausted by simple and efficient enough arrangements.
Furthermore in international publication WO 2006/005788 there has been presented a method and arrangement for the removal of surface scum, which enable controlling of overflow from a primary space to a secondary space of surface scum particularly in order to minimize the liquid getting drifted therewith. This has been carried out by adjusting a surface level of the primary space by means of a flow balancing assembly connecting the primary space and the second surface chute arrangement and/or by using an adjusting device existing in the wall defining the primary space and the secondary space. The solution in question has been found very operative in practice, whereby, however, there has been found a further need for improvement in guiding of passage of the surface scum in the primary space towards the secondary space.